Who is The Three Gods from The Good Person of Szechuan and what is their importance?

The three gods make their journey in order to find at least one good person on the earth. They stay with Shen Teh and commend her hospitality. They ignore, however, the good deeds she performs in her neighborhood for the poor and abject. They later appear to Wang, and they tell him that a good person will always make the right decision, no matter the consequences. In the end, the three gods fail to realize it is impossible for humans to always make good choices, when there are so many bad people taking advantage of the good people.